The present invention relates to a device and method for scrapping and destroying tires with metallic cords, using electric discharges. The device is designed to separate metal and rubber components for their subsequent separate salvage and retrieval, utilizing known, conventional techniques, such as melting the metal and forming rubber crumb for use in the production of flexible pavement and rubber articles, such as roofing, hydraulic insulating materials, heat-insulating and sound-insulating materials.
Pneumatic vehicle tires that cannot be repaired or refurbished are a major source of the environmental pollutants and are, at the same time, however, a valuable source of recoverable and recyclable refuse. That is why the recovery of salvageable materials from such tires is a critical issue, especially in the more economically developed, and higher population density countries. Technological means for the solution of this problem must be adapted compatible basic conditions, such as ecological safety, economy and possibility of sufficiently complete salvaging of tires.
Typical tires manufactured today, having metallic cord reinforcements, usually referred to as xe2x80x9csteel-beltedxe2x80x9d tires, have an outer tread surface that comes in contact with the road. The tread is made from rubber only. The tread is attached to two shoulders, one at either side of the tread strip. Each shoulder has a sidewall attached to it. Each sidewall terminates in a bead, which enables the tire to be mounted on and fit into an outer edge of a wheel. The tire has an inner carcass that is typically made from a corded textile material. The breaker is a bracing ply found below the tread. In steel-belted radial tires, the breaker typically includes two layers of metallic cord material. Each layer contains a plurality of separated metallic wires that are surrounded by rubber. The wires in adjacent layers are typically oriented at an angle of about xc2x170xc2x0 with respect to a central geometric axis through the tire.
The simplest solution to the problem of the disposal of scrap tires, incineration, was widely used in many countries for many years. Up to 45% of worn-out tires in Germany and The Netherlands, and up to 40% of worn-out tires in Japan used to be incinerated (Tire Recycling Plant Tire Up, xe2x80x9cModern Tire Dealerxe2x80x9d, 1987, No. 8, p. 6). However, incineration is accompanied by the formation of a complex of toxic substances, particularly sulfur-containing substances, the release of which into the atmosphere is an environmental hazard that far outweighs any benefits achieved in the recovery of residual metals and the recovery of heat generated by the incineration process.
Therefore, it is more preferable to utilize other technological means to provide for the destruction of worn-out tires and achieve the separation and recovery of useable rubber and metal by-products.
One alternative to incineration that is widely practiced is mechanical crushing. Devices for mechanically crushing tires, which operate at ambient temperature are known (xe2x80x9cGummibereitungxe2x80x9d, 1987, Bd. 63, No. 10, p. 102-104). Other known devices are based on the deep freezing of the rubber component of the tires (Vorbildliches Recycling alter Reifen in Kall/Eitel, xe2x80x9cGummibereitungxe2x80x9d, 1987, Bd. 63, No. 10, p 97-100). Both mechanical crushing and deep freezing processes are followed by the separation and recovery of components, however, the yields of useable materials are typically quite low.
Processes based on the mechanical shredding of resilient rubber from tires, together with the metallic cord content, followed by crushing of the shreds, are generally highly energy consuming and have low efficiency. Because of the low heat transfer coefficient of rubber, the size of tire shreds to be frozen in deep freezing processes is limited to particles that have a maximum dimension of not greater than 3 cm, which also leads to an increase in the specific energy consumption for shredding and mechanical crushing. Frozen pieces of rubber also do not result in homogeneous (in terms of size grading) semi-finished products. This also results in a certain portion of rubber being discharged together with the metal during magnetic separation.
It is also known that an electric-heat pre-treatment of tires reduces the loss of rubber and simplifies the separation of metallic cords.
In the simplest of devices utilizing this process (DE 2900655 Al), the device itself typically includes the following components:
first conveying means for delivering tires that have had their sidewalls removed to further processing equipment for complete destruction;
a tire destruction system in the form of a current source provided with contacts for connection to metallic cords, such that the source heats the cord wire and causes burning of the adjacent plies of rubber; and
second conveying means for transporting and discharging the by-products of tie destruction from the processing area.
Use of an electric-heat treatment based tire destruction process, over a prolonged period of time, is characterized, however, by one of the above-mentioned disadvantages of tire incineration, albeit to a lower degree, namely, with the discharge of toxic materials that pollute the atmosphere and are dangerous to workers and persons in general. In addition, processes requiring lengthy periods of heating are not efficient and have a high specific energy consumption. Moreover, the devices of such processes are effective only in processing those tires having metallic cords that thread through the breaker strip from one sidewall to the other, because only in such case, can substantially all cord wires be brought into secure electrical contact with a source of current, after the sidewalls have been cut off. Finally, the use of such a device creates a problem of separate salvaging of cut-off sidewalls.
Devices for heating the entire mass of metal inside the tires are known, and are provided, for example, in devices that utilize inductive heaters, such as are disclosed in German patent DE 3911082 A1 and European patent EP 0478774 A1. There are, however, a number of other disadvantages in the electric-heat destruction of tires that are more difficult to overcome.
Such other disadvantages can be overcome with the help of electric pulse destruction of tire cord wires. Such a process generally includes a step of passing short pulses of electric current of high density and power through the cord wires. This leads to heat emission, mainly at the boundaries of crystal grains of metal, and to the destruction of tire cord wires in a dangerous and potentially explosive manner.
One such device of this type is known in the art and is described in Russian patent RU 2050287. The device includes:
means for cutting off tire sidewalls (in one embodiment);
means for delivering tires for destruction;
a tire destruction system comprising:
a pulse-discharge unit based either on a capacitor bank or on an accumulative reactive LC-circuit, and
an axially symmetrical means for galvanic or electromagnetic connection of the pulse-discharge unit to a metallic cord made respectively either in the form of two current conducting members for fixing the tire to be destroyed mounted for relative reciprocating motion and having the working surfaces in the shape of truncated cones facing each other (by the smaller bases in particular) or in the form of the primary winding of a transformer that in any case must be coaxial with the tire to be destroyed and for this reason can be located either along the geometric axis of the tire or encompass the tire;
at least one means for discharging the products of the destruction from the working area and, preferably, protective chamber.
The tire destruction system based on the accumulative reactive LC-circuit and the means for electromagnetic connection of the pulse-discharge unit to a metallic cord in the form of the primary winding of a transformer seems to be preferential as far as it is serviceable for destroying the whole tires a priori. However, the experimental study has shown that the galvanic connection between the pulse current source and metallic cords (with the sidewalls being cut off) is more profitable in terms of energy than the electromagnetic connection.
Actually, in the case of the galvanic connection of tire cord wires to the bank of capacitors, the specific consumption of electricity per unit of mass of metal segregated from the tires essentially does not depend on the whole mass of metal in the tire and happens to be the lower the higher is the energy density in the pulse and the shorter is the pulse. Moreover, eddy currents can be induced powerful enough to destroy the cord wires even in that portion of cords (minor as a rule) that fails to come in galvanic contact with the pulse-discharge unit (e.g., because of inconvenient fit to the current conducting fixing members).
As for electromagnetic (transformer) transfer of energy from a reactive LC-circuit to metallic tire cord, the greater the mass (and inductance) of the metal contained in the tire to be destroyed, the less is its efficiency.
However, there are tires wherein cutting off the sidewalls does not reveal the ends of a large proportion of cord wires that cannot be efficiently destroyed with galvanic connection to the pulse-discharge unit by the known methods. These are large size tires, as a rule, whose destruction in the whole state (without cutting off the sidewalls) in accordance with a xe2x80x98transformer circuitxe2x80x99 is also not efficient because of the mentioned reasons.
Thus, the improvements in the design of a device for the electric pulse destruction of tires having metallic cords after cutting off the sidewalls, according to the present invention, are a great improvement in the state of the art.
Accordingly, it is one object of the present invention to develop a device for scrapping and destroying rubber tires, which contain metallic cords, that is capable of salvaging and separating the rubber and metal components as useable by-products.
It is another object of the present invention to develop a device that is capable of salvaging and separating the rubber and metal components of the breaker layer and the sidewalls.
It is another object of the present invention to develop a device and method for scrapping and destroying tires, wherein metal separation of each part of the tire is accomplished separately
The present invention is based on the need for creating, by way of improving the design on the whole and particularly the axially symmetrical means for galvanic connection of the pulse-discharge unit to a metallic cord, firstly, such device for destroying tires with metallic cords using electric discharges, which provides for effective destruction of tires of different sizes whose substantial portion of cord wires cannot be brought into direct galvanic contact with a pulse current source after cutting off the sidewalls, and secondly, creating, by way of enhancing this device with a means for destroying the cut-off sidewalls, a still more improved device that provides for substantially complete separation of metal from rubber in tires.
The first main part of the problem is solved in that in the device for destroying tires with metallic cords using electric discharges comprising means for cutting off the sidewalls of tires, means for delivering tires with cut-off sidewalls for destruction, a tire destruction system in the shape of a pulse-discharge unit based on capacitors which is provided with an axially symmetrical means for connection to metallic cords in the form of two current conducting fixing members having the shape of truncated cones on the side of their working surfaces and at least one means for discharging the products of the destruction from the working zone, according to the invention, the axially symmetrical means for connection of the pulse-discharge unit to metallic cords is provided with an additional current conducting protrusion which is arranged coaxially relative to both current conducting fixing members, being galvanically connected to one of them and electrically isolated from the other.
Actually, the pulse current flows in the opposite directions through said protrusion and through the cord wires of the tire being destroyed when the device of the invention is used. Such arrangement provides for the simultaneous achievement of two technological effects:
firstly, the combined electrical inductance of said means for connection of the pulse-discharge unit to a metallic cord and the very metallic cord decreases and, correspondingly, the duration of the pulse shortens while the amplitude and density of current increase therein;
secondly, according to the Ampere law, the conductors along which the currents flow in opposing directions come in mechanical interaction, and hence a repulsive mechanical impulse (so called xe2x80x9cmagnetic impulsexe2x80x9d) appears between said protrusion and all cord wires of the tire being destroyed, said impulse growing in proportion to the increase in the amplitude of the current in the destructive pulse.
Combination of said effects allows the efficiency of separation of metallic cord from rubber to be essentially increased when destroying tires (especially of a large size) and particularly in case of incomplete galvanic contact between cord wires and the pulse-discharge unit.
Additional embodiments of the apparatus of the present invention, which contain additional features, which may be combined, are within the scope of the invention.
The first additional characteristic feature consists in that the additional current conducting protrusion is made in the shape of a central rod, which is preferable in destroying small size tires.
The second additional characteristic feature consists in that the central rod is provided with a support platform, whereon a dielectric pad and one of the fixing members are placed, and is rigidly secured to the immobile base at one side, while it is operatively connected to the second fixing member at the other side. Such arrangement of the central rod and its interconnections with the remaining parts of the axially symmetrical means for connection of the tires to be destroyed to the pulse-discharge unit simplifies the delivery of tires and increases reliability of their holding at the discharge of capacitors.
The third characteristic feature, additional to the second feature, consists in that the central rod and the second fixing member are made in the form of a xe2x80x98bolt-nutxe2x80x99 couple, which allows tires of different standard sizes to be destroyed by controlling the force of the contact between the cut sidewalls of tires and fixing members depending on the rigidity of tires.
The fourth characteristic feature, additional to the second feature, consists in that the central rod is provided with a stop in the middle part, while the second fixing member is made in the form of a knock-down coupling. This arrangement is preferable in a line destruction of tires of the same standard size.
The fifth additional characteristic feature consists in that the additional current conducting protrusion is made in the shape of a peripheral ring, which allows a substantial simplification of the means for guarding the zone of the tire destruction.
The sixth characteristic feature, additional to the fifth feature, consists in that the peripheral ring is made in the form of the side wall for a xe2x80x98bottom-coverxe2x80x99 couple comprising two parts overlying one another and having ring shaped inner sides as well, which essentially turns this part of the device into a protective chamber.
The seventh additional characteristic feature, directed to the solution of the second part of the problem, consists in that the device for destroying tires with metallic cords using electric discharges is additionally provided with a system for destroying the cut-off sidewalls, which comprises an inductor connected to the pulse-discharge unit, a support assembly for the cut-off sidewalls and a clamp mounted for reciprocating motion. Thus, a complete destruction of tires with the use of electric discharges is provided.
The eighth characteristic feature, additional to the fifth feature, consists in that the system for destroying the sidewalls is provided with a second inductor also connected to the pulse-discharge unit, which facilitates destroying the sidewalls having the remainder of cord wires.